This invention relates to earth boring by the rotary system of drilling and more particularly to mud saver valves or kelly foot valves, used at the lower end of the kelly to retain the drilling fluid in the kelly when the connection between the valve and drill pipe is broken.
The function and operation of mud saver valves and the development of the art by early workers in this field are discussed in U.S. Pats. No. 3,698,426 and 3,738,436 issued on the applications of Litchfield and Scott and in U.S. Pat. No. 3,698,411 issued on the application of William R. Garrett, the disclosures of these three patents being incorporated herein by reference. The prior art cited in these three patents and the references cited against them during their prosecution may be referred to for further background.
A commercial embodiment of the mud saver valve disclosed in the aforementioned Garrett patent, hereinafter sometimes referred to as the Model A valve, is shown in FIG. 1 of the accompanying drawings. As in the aforementioned Garrett patent the valve includes a top sub whose lower end provides a poppet valve seat, the sub being screwed into a tubular body in which the poppet valve closure moves axially. The latter comprises a ring at the upper end of a tubular stem and a frangible breakout cap with a tubular guide slidable in the stem. The cap and ring form an upwardly opening check valve. The stem has a radial flange moving in a counter bore in the body and is sealed to the body at the flange and below the counter bore to define a sealed chamber at atmospheric pressure. The seals are effected by snap-on unidirectional double lip type plastics material seal rings, namely seals with the trademark Polypak made of polyurethane filled with molybdenum disulfide; there being an O-ring spreader between the two lips. The drawing scale is such that these details are not shown. Within the chamber is a coil spring urging the poppet valve upwardly against the seat on the top sub. Compared to the Garrett patent construction, the breakout cap of the upwardly opening check valve closure in the downwardly opening poppet valve closure is of more gently sloping convexity (viewed from above), since a thicker drilling fluid boundary layer over the cap will streamline the flow. The tubular poppet stem is in two pieces for easy replacement of the upper foraminous crossover portion wherein the fluid moves from the outside to the inside of the tubular stem and is filtered or screened in the process. There is a threaded pin on the lower end of the upper portion to which is screwed a box on the upper end of the lower sealed chamber forming portion of the stem. There is a J-slot in the lower end of the stem for engagement with a pulling tool during assembly. By this means the spring can be compressed enough for the top sub threads to engage with the body. This eliminates the need for a separate threadably connected bottom sub. Therefore the bottom pin connector is made integral with the valve body. A rubber protective sleeve is disposed around the sub that forms the mud saver valve body.
Around 1971 or 1972 several hundred or so Model A valves were made and sold and used. Difficulties experienced with the Model A valve included: (1) frequent manufacturing departures from design at the metal-to-metal juncture of poppet valve seat and closure, resulting in leakage, (2) erosion of this same metal-to-metal juncture during usage, (3) turbulence in the drilling fluid flow-stream due to wings on the screw cap of the check valve, (4) release of the rubber threads on the screw cap, (5) canting of the check valve closure, (6) displacement from intended position on the lower or chamber forming portion of the stem of the snap-on upper and lower plastics material O-ring seals, such displacement occurring when the stem and seal assembly is inserted in the valve body, the seal rings rotating in their grooves or rolling out of their grooves, and (7) loss by the customer of the assembly tool that is used to engage the lower end of the valve stem to draw it down and pre-compress the valve spring sufficiently to allow the top sub to be screwed into the valve body.
In an effort to overcome the foregoing difficulties a construction hereinafter sometimes referred to as the Model X valve was invented, a principal feature of which is the provision of screw-jack means in the valve stem for compressing the valve spring during assembly. A bridge forming one element of the screw-jack means is somewhat similar to a construction that has been suggested for use in a vibration dampener, but which is still in the development stage. Another feature of the Model X valve is that seal ring displacement during assembly is overcome by making it unnecessary to stretch the plastics material seal rings during assembly. It was found that such rings take a substantial time to recover their initial diameter after being stretched to slip over the valve stem and their protusion was the cause of their later displacement when the stem was assembled into the valve body. A further feature of the Model X valve is a replaceable non-metallic seat provided in the top sub to eliminate the metal-to-metal juncture. All of this was the work of the present inventor. The Model X valve also incorporated a new construction for the check valve which was attributable to the inventor who is the applicant in the aforementioned Williamson application filed concurrently herewith. The rubber screw cap threads were replaced by metallic threads on the metal breakout disc, and the check valve guide stem was lengthened. The rubber cover was bonded to the breakout disc and its outer periphery was provided with a skirt overlying the threaded juncture of the breakout disc and the check valve closure ring. The skirt provides also a means to grip the cap during assembly, the rubber wings having been eliminated.
Around June 1972, about five Model X valves were built and put out for test without any remuneration to the manufacturer. It is understood that one of the recipients of these Model X valves received some rental from a user in about December, 1972. The valves ultimately were all received back by the manufacturer. In view of the tests changes were made, the new construction, sometimes hereinafter called the Model B, being for commercial production. It incorporates inventive features of the Model X valve and further inventions of the aforesaid Williamson. The aforementioned Williamson copending application is directed to these further improvements as well as those features of the Model X valve which were the invention of Williamson. The present application claims those features of the Model X valve which are the invention of the present applicant.